A mysterious coolant leak not directly under the expansion tank. What is it? on 1996 GMC Suburban 2500

It seems I have a coolant leak(only when the engine is running) which seems to be coming from a water line junction or distribution piece that looks maybe to be plastic. It is under the resevoir tank/ air cleaner inlet, down about a foot or so. It has a hose(maybe 2) coming into it from the radiator and 2 hoses leaving it going into the firewall. It has a device that looks like it might be some sort of vacuum switch with a wire or small hose leading off of it, right beside this junction. Is this associated with the heating system? What would this part be called so that I can order a new one? Apparently, it has a crack in it and leaks when under pressure.

I had the same problem. There are two water hoses that run back to the rear heater. There are plastic "T's" under the air cleaner box and these "T's" will break or split causing coolant to exit, sometimes quickly. An easy fix. Buy two "T's" at a time and replace them both. Remove air cleaner box and the "T's" are right there and easy to get to.